Electrically driven hydraulic construction machine

Abstract

To reduce an increase in the electric power consumption of an electric motor according to the state of an electric power source at the start of driving of an actuator, and make it possible to use devices in an appropriate state in an electrically driven hydraulic construction machine including a driving system that drives a hydraulic pump by using the electric motor. For this purpose, a controller 50 sets a target relief pressure of a relief valve 3 to a normal relief pressure Pn (first relief pressure) when an operation lever device 44 is not being operated and a storage amount SOC(t) of a battery 62 (the state quantity of an electric power source) is equal to or larger than a threshold S 1 , and sets the target relief pressure to a reduced relief pressure Pr(t) (second relief pressure) lower than the normal relief pressure Pn (first relief pressure) when the operation lever device 44 is not being operated, and the storage amount SOC(t) of the battery 62 (the state quantity of the electric power source) is smaller than the threshold S 1.

The invention claimed is: 
     
       1. An electrically driven hydraulic construction machine comprising:
 a hydraulic pump; 
 an actuator driven by a hydraulic fluid delivered from the hydraulic pump; 
 an operation lever device that instructs an operation speed and direction of the actuator; 
 an operation state sensor that acquires operation state information about the operation lever device; 
 a relief valve that is connected to a hydraulic line connecting the hydraulic pump with the actuator, and discharges the hydraulic fluid in the hydraulic line to a tank when a pressure in the hydraulic line has reached a preset target relief pressure; and 
 an electric motor that is supplied with electric power from an electric power source, and drives the hydraulic pump, wherein 
 the electrically driven hydraulic construction machine further comprises a controller that changes the target relief pressure of the relief valve on a basis of the operation state information and a state quantity of the electric power source, and 
 the controller is configured to 
 set the target relief pressure to a first relief pressure when the operation lever device is not being operated and the state quantity of the electric power source is equal to or larger than a preset threshold, and to set the target relief pressure to a second relief pressure lower than the first relief pressure when the operation lever device is not being operated and the state quantity of the electric power source is smaller than the threshold. 
 
     
     
       2. The electrically driven hydraulic construction machine according to  claim 1 , wherein
 the controller is further configured to 
 make the target relief pressure the first relief pressure by increasing the target relief pressure at a predetermined rate in a case in which the operation lever device is operated to start driving the actuator when the target relief pressure is the second relief pressure. 
 
     
     
       3. The electrically driven hydraulic construction machine according to  claim 2 , wherein
 the controller is further configured to 
 calculate a relief pressure increase amount that decreases as the state quantity of the electric power source decreases for each predetermined time, and make the target relief pressure the first relief pressure by adding the relief pressure increase amount to a current value of the target relief pressure, and increasing the target relief pressure at a predetermined rate in a case in which the operation lever device is operated to start driving the actuator when the target relief pressure is the second relief pressure. 
 
     
     
       4. The electrically driven hydraulic construction machine according to  claim 2 , further comprising:
 a pressure sensor that senses a delivery pressure of the hydraulic pump, wherein 
 the controller is configured to 
 set the target relief pressure to a current value of the target relief pressure when a difference between the current value of the target relief pressure and the delivery pressure of the hydraulic pump sensed by the pressure sensor is equal to or larger than a preset decision differential pressure. 
 
     
     
       5. The electrically driven hydraulic construction machine according to  claim 2 , further comprising:
 a pressure sensor that senses a delivery pressure of the hydraulic pump, wherein 
 the controller is configured to 
 set the target relief pressure to a value obtained by adding a preset decision differential pressure to the delivery pressure of the hydraulic pump until the target relief pressure lowers to the second relief pressure when a difference between a current value of the target relief pressure and the delivery pressure of the hydraulic pump sensed by the pressure sensor is equal to or larger than the decision differential pressure. 
 
     
     
       6. The electrically driven hydraulic construction machine according to  claim 1 , wherein
 the electric power source is a storage apparatus that stores electric power, 
 the state quantity of the electric power source is a storage amount of the storage apparatus, and 
 the controller is configured to calculate the storage amount on a basis of a storage amount signal transmitted from the storage apparatus. 
 
     
     
       7. The electrically driven hydraulic construction machine according to  claim 1 , wherein
 the electric power source is an external electric power converting apparatus that converts electric power supplied from an outside of a machine body, and supplies the electric power to the electric motor, 
 the state quantity of the electric power source is an available electric power supply of the external electric power converting apparatus, and 
 the controller is configured to calculate the available electric power supply on a basis of an electric power signal transmitted from the external electric power converting apparatus. 
 
     
     
       8. The electrically driven hydraulic construction machine according to  claim 1 , wherein
 the electric power source is an external electric power supplying apparatus that is installed outside a machine body, and supplies electric power to the electric motor, 
 the state quantity of the electric power source is an available electric power supply of the external electric power supplying apparatus, and 
 the controller is configured to calculate the available electric power supply on a basis of an electric power signal transmitted from the external electric power supplying apparatus.